Chapter 16Roofing
Roofing
First line of defense against the weatherPrecipitation (Rain, snow)SunThermal Transmission
Subjected to extreme heat and cold
Surface can have wide temperature swings
Roof Groups
Steep Roofs
Low-Slope Roofs
Steep Roofs
Drain quicklyLess opportunity for gravity or wind to push/pull water
through the roofing material
Facilitate the use of shinglessmall, overlapping roofing unitsAdvantages:
Can be inexpensive, easy to handle & install, Accommodate thermal expansion/contraction & structural
movement Vents water vapor easily Visible - Aesthetics
Low Slope Roofs
Low-Slope RoofsAdvantagesCan cover a “large” horizontal surface (vs steep)Simpler geometry, often less expensiveRoof can have other functions - patio, decks, parking, ...
DisadvantagesWater Drains SlowlySlight Structural Movements Tear the MembraneWater Vapor Pressure Can Blister & Rupture the Membrane
Low-Slope Roof Components
Structural Support - Deck
Thermal Insulation
Vapor Retarder
Roof Membrane
Roof Ballast
Drainage
Flashing
Roof Deck
Materials (Plywood, OSB, Steel, Concrete)
Performance requirementsSupport Roof LoadingResist UpliftSloped for Drainage Expansion & Contraction - Roof & StructureSmooth, Clean SurfaceDry Prior to Membrane Placement
Thermal Insulation
Resist Heat Transfer
Location / PlacementBelow the DeckBetween the Deck & MembraneAbove the Membrane
Rigid Insulation Attachment (adhered or mechanically attached)
‘Rigid’ roof insulation being placed over metal decking(mechanically fastened to decking)
Vapor Retarder
Purpose - Prevent transmission of Water VaporLocation / PlacementGenerally Below the Insulation
Material - hot mopped felts most common
Insulation VentilationRoof Vent
Roof Membranes
Three Categories
Built-up Roof (BUR) Membrane
Single-Ply Roof Membrane
Fluid Applied Roof Membrane
Built-up Roof Membrane
“Multiple plies of asphalt-impregnated felt bedded in bitumen”
Application:
Felts laid in Hot Asphalt (or coal tar)
Overlapping Layers
Forms a “laminated” membrane typically 2-4 plies thick
Asphalt Felts
Felts being ‘Hot-Mopped’
Kettle for heating the bitumen and pumping it to the roof
Single-Ply Roof Membrane
“Sheet materials that are applied to the roof in a single layer”
Attached to the Roof:
Adhesives
Ballast Weight
Concealed fasteners
Single Ply Materials
Thermoplastics May be softened and joined by heat or solvent
weldingPolyvinyl Chloride (PVC) – widely used, Polymer-
modified bitumens, PVC alloys, etc.
Thermosetting Can not be softened - must be joined by adhesives
or pressure sensitive tapesEPDM (the most widely used), Neoprene, CPE, etc.
The following series of photos are from the roofing operations of a 47,000sf single story retail facility.
The roof system: Uses rigid insulation over metal decking with a:Thermoplastic Membrane where the Sheets are mechanically fastened to the structure
and the seams welded
Metal DeckWelded to Structure
2” Rigid InsulationMechanically Fastened
Insulation Fastener
Insulation Fastener - penetrates through the insulation to the metal deck
Roof Membrane Rolls
Lap Markings
FastenerLocations
Membrane being rolled out
Rolled out & leading edge attached
Membrane Mechanical Fastener(penetrates the insulation and anchors to the metal deck)
Membrane Lap
Welding Machine(welds the seams)
Lap Welded
Membrane Flashing @ Curbs
Fluid-Applied Membranes
“Membranes applied with a roller or spray gun and cure to form a rubbery membrane”
Uses
“Complex shapes that are difficult to roof by conventional means”
Examples: Domes and shells
Ballast & Traffic Decks
Ballast MaterialStone aggregatePrecast concrete blocks or Pavers
PurposeHold down membraneProtect membrane from ultraviolet lightProtect membrane from physical wear
Traffic Decks – installed over membranes for walks, terraces, drives, etc.
Roof Flashing - Roof Edge
Edge Flashing
Expansion Joint - Building
Building/Roof Expansion Joint
Area Divider
Area Divider
Parapet
Parapet Flashing
Roof Drain
Roof Drain
Roof Penetration
Penetration - Vent
Steep Roofs
Roofs with a pitch of 3:12 (25%) or greater
Three General CategoriesThatchShinglesArchitectural sheet metal
Insulation & vapor retarderTypically installed below the roof decking
Decking – typically plywood or OSB
Shingles
“applied to the roof in small units and in overlapping layers with staggered vertical joints”
MaterialsWood (shingles & shakes)AsphaltSlatesClay TilesConcrete Tiles
Cedar Shakes (split rather than sawn)•Natural decay resistant wood•Moderately expensive•Fire Resistance low unless treated
Asphalt Shingles•Die-cut from sheets of asphalt-impregnated felt faced with mineral granules•Typical size – 12”x36”
Different AsphaltShingleProfiles & Colors
Slate:•Fire-resistant•High initial cost, but long life
Slate Roofing & Copper Flashing
Slate w/ Predrilled Holes
Clay Tiles
Concrete Tile
Asphalt Felt – typically adhered to the deck prior to the installation of the shingles
Roofing FeltAsphalt Shingles - Packaged
Laid from the Eave up
Ridge Treatment &Valley Flashing
Architectural Sheet Metal Roofing•Materials – typically thin sheets of aluminum or galvanized steel•Coatings – typically a polymeric available in various colors•Seams – raised interlocking edge seams •Fasteners – concealed or exposed fasteners with rubber washers
Lead Coated Copper
Roofing & the Building codes
Classified based upon Flame Spread resistanceClass A: effective against severe fie exposure
Slate, concrete & clay tiles, asphalt shingles with glass felts, & most built-up and single ply
Class B: effective against moderate fire exposure Many of the built-up & single ply, metal roofs, asphalt
shingles based upon organic felts
Class C: effective against light fire exposure Fire retardant wood shingles & shakes